It is known that the printing machines utilized for executing prints of the above mentioned type, also called flexographic printing machines, comprise a drum around which the web travels and at least one cliche cylinder, on which the printing ink is distributed and from which the ink is transferred to the web to be printed. In order to obtain the distribution of the ink on the cliche cylinder, it is used an unit, commonly called “colour unit”, comprising a reservoir for the ink or “fountain”, a distributor cylinder or “anilox cylinder” which receives the ink from the reservoir and transfers it by contact to the cliche cylinder, and two blades, or doctors, disposed and acting between the fountain and the anilox cylinder.
In FIG. 1 is represented, schematically, a typical flexographic printing machine with four colour units. In this scheme, (RI) indicates the transmission roll onto which the web (N) to be printed travels, which moves in the direction of the arrow (Z); (C), (D) and (E) indicate three guiding rolls of the web (N) disposed upstream of the roll (RI); (F) and (G) indicate two guiding rolls of the web (N) disposed downstream of the roll (RI); (H), (L), (P) and (Q) indicate four identical colour units symmetrically disposed around the roll (RI); (CD) indicates an anilox cylinder; (CL) indicates a cliche cylinder, (LS) and (LI) indicate two doctors disposed and acting between the fountain (U) and the anilox cylinder (CD); (S) indicates a support structure of the doctors (LS, LI). The two doctors delimitate, in cooperation with the structure (S) and the surface of the anilox cylinder (CD), the fountain (U) in which is contained the ink for the same cylinder (CD). The two opposite bases of the fountain (U) are closed by relevant tight plates or gaskets. (M) indicates the rotation direction of the roll (RI).
The cliche cylinder is constituted by a cylindrical body with smooth surface, onto which there is movably fitted a jacket provided with reliefs acting to form the patterns and the writings to be printed. In such way, for varying the printing effects, it is sufficient to remove the jacket from the cylinder and to substitute it with a different jacket, afterwards called “cliche jacket”.
This operation concerns, mostly, all the colour units of the machine. The latter is stopped during the substitution of the cliche jackets, with a loss of production corresponding in extent to the time required for the substitution.
In order to substitute of the cliche jacket, it is necessary that the operator dismounts the support of the cylinder utilizing, at least in part, manual tools; this requires a time as great or as small as the skill of the operator and it can involve risks of damage for the parts which are dismounted and afterwards remounted.
The same drawbacks relates to the distributor units utilized, for example, for distributing glue or other liquid substances on web-shaped materials in movement and structured as the before said colour units, that is provided with a cylinder onto which it is movably fitted a jacket (called also in this case “cliche-jacket” because it is provided with reliefs apt to allow the distribution of the substance only on preset points of the web and not over the whole surface of the same) and a distributor cylinder which receives the substance from a relevant reservoir and, by contact, transfers it to the cliche cylinder.
Distributor units are described in U.S. Pat. No. 6,615,716, EP741009 and EP596244.